1. Field of the Invention
The present invention relates to an overcurrent detecting circuit, and test system and process for testing overcurrent detecting function. More specifically, the present invention relates an integrated MOSFET circuit having an overcurrent detecting circuit section of a mirror MOSFET, and test system and process for testing integrated circuit devices of such a type.
2. Related Art
A MOSFET integrated circuit device of one example comprises a main MOSFET having a drain connected with an output terminal and a source connected with a ground terminal, a mirror MOSFET, a current sensing resistor, a comparator for detecting an overcurrent condition by comparing a potential at the source of the mirror MOSFET with a reference potential of a reference voltage source, and a control circuit section for protecting the circuit by turning off the main MOSFET in case of the overcurrent condition. The drains of the main MOSFET and the mirror MOSFET are connected together to the output terminal which is connected through the load to a power source. A drive current flows along a path of power source.fwdarw.load.fwdarw.output terminal.fwdarw.main MOSFET.fwdarw.ground terminal.
In a test system used in a fabricating process, for testing the overcurrent detection function of such a MOSFET integrated circuit device, it is required to supply a drive current at an overcurrent level from the output terminal to the main MOSFET, and checks if the main MOSFET is turned off by the overcurrent detecting circuit. In consideration of requirements on the main MOSFET, the current threshold above which an overcurrent condition is judged to exist is set at a high magnitude of about several amperes or higher, near the maximum current which the main MOSFET, and bonding wires of the output terminal and the ground terminal can handle. Application of such a high drive current in a package testing operation is liable to reduce the lifetime of a socket used for connection of a semiconductor package.
Moreover, a probe test of such an integrated circuit device in the state of a wafer is infeasible because a current to be detected as a overcurrent exceeds an allowable current of a contact portion between a pad of the semiconductor device and a probe of the tester. Recently, many semiconductor devices are used in the form of bare-chip mount without packaging. However, the testing of overcurrent detecting function is not possible because of lack of an appropriate way for probe testing.